Japanese Encephalitis

Japanese encephalitis is a disease transmitted when an infected mosquito bites a human or other animal. The mosquitos most likely to be infected are those that breed in rice fields.

Japanese encephalitis virus is NOT transmitted from person-to-person, but can be transmitted from domestic pigs or wild birds to humans. Japanese encephalitis is the leading cause of viral encephalitis in Asia with 30-50,000 cases reported annually. Outbreaks of JE are usually contained to small areas but can occur in multiple areas, especially during the rice growing season. They usually do not last more than a couple of months, dying out after the majority of the domestic pigs have become infected. Birds are the natural hosts for Japanese encephalitis. Epidemics occur when the virus infects mosquitos which infect domestic pigs and wild birds which live with the human population.

Countries which have had major epidemics in the past, but which have controlled the disease primarily by vaccination, include China, Korea, Japan, Taiwan and Thailand. Other countries that still have periodic epidemics include Viet Nam, Cambodia, Myanmar, India, Nepal, and Malaysia.

Mild infections of JE can occur without apparent symptoms other than fever with headache. More severe infection is marked by quick onset, headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions (especially in infants) and spastic paralysis.

Japanese encephalitis vaccine is recommended for persons who plan to reside in areas where Japanese encephalitis is endemic or epidemic during a transmission season. Japanese encephalitis vaccine is NOT recommended for all travelers to Asia. The risk for both residents and travelers from other countries varies according to the length of exposure, conditions of housing, nature of activities, and the possibility of unexpected travel to high-risk areas.

In general, Japanese Encephalitis vaccine should be offered to persons spending a month or longer in endemic areas during the transmission season, especially if travel will include rural areas. Under specific circumstances, vaccine should be considered for persons spending <30 days in endemic areas, e.g., travelers to areas experiencing epidemic transmission and persons whose activities, such as extensive outdoor activities in rural areas, place them at high risk for exposure. In all instances, travelers should be advised to take personal precautions to reduce exposure to mosquito bites.

JE-Vax is given in 3 doses over a period of 4 weeks to persons under 17 years of age.

Available as IXIARO for ages 2 months and older as two doses given 28 days apart.

This vaccine may have serious side effects, therefore risk of exposure must be carefully weighed against this risk when considering the Japanese Encephalitis vaccine.